Oxygen consumption of the West African blood clamAnadara senilis

The West African blood clamAnadara senilis (L.) is one of a small number of bivalve species which have haemoglobin in their haemolymph. In the investigation reported here, in which the musselMytilus edulis (L.) was also studied for comparative purposes, it was shown thatA. senilis was an oxygen regulator between oxygen tensions corresponding to 50 and 100% air saturation. Oxygen uptake increased by about 128% after 24 h at zero pO₂; although the haemoglobins ofA. senilis were found to be responsible for about 34% of oxygen uptake at 25°C (a proportion unaffected by pO₂), there was clearly insufficient haemoglobin present in the haemolymph to act as an effective oxygen store during prolonged exposure to anoxic conditions.     

Metabolic responses to changing environmental conditions in the brackish water polychaetes Marenzelleria viridis and Hediste diversicolor

The metabolic strategies of the polychaete Marenzelleria viridis (Verrill 1873), a successful immigrant into Baltic shallow eutrophic coastal waters with meso-to oligohaline salinities since the 1980's, were determined by simultaneous calorimetry and respirometry. Resistance to oxygen deficiency under varying ecological conditions was also examined. The results of the studies with this immigrant were compared to those with the common indigeneous polychaete Nereis (Hediste) diversicolor (O.F. Müller). At 10 and 20 °C and the average habitat salinity of 5 M. viridis gradually reduced its metabolic activity with declining oxygen partial preessures (pO₂), whereas H. diversicolor maintained its metabolic activity. The metabolism of both species remained fully aerobic down to a pO₂ of 2 kPa. An additional hyposmotic stress of 0.5 salinity at a temperature of 20 °C led to a decrease in the rate of oxygen consumption in H. diversicolor below a pO₂ of 10 kPa, whereas metabolic heat dissipation remained constant. M. viridis, however, further reduced both, metabolic heat dissipation and oxygen consumption. The metabolic rates of both species under anoxia were similar, amounting to ca. 20% of the normoxic rate. The resistance of the two species to oxygen deficiency was also similar, ranging between 21 and 290 h (median survival time LT₅₀), depending on temperature and salinity. Specimens used in the present study were collected from the Southern Baltic coastal inlet of Darß-Zingster-Boddenkette during 1992 and 1993.     

Upper temperature tolerances of some European molluscs. I Tellina fabula and T. tenuis

The upper temperature tolerances of two European species of Tellina from populations near the northern and southern limits of their geographical range are compared by means of median lethal temperature (LT₅₀), and median burial temperature (BT₅₀) determination for periods of exposure up to 96 h. The influence of previous acclimation temperature, and salinity within a limited range, on these determinations is also considered. T. fabula Gmelin, which is found in deeper water throughout its range, shows a lower thermal tolerance than T. tenuis da Costa. Both species display a significant effect of previous acclimation temperatures, the effect on the burrowing responses being greater than that shown by LT₅₀, and in both species the thermal tolerance of individuals from Mediterranean populations is greater than that of individuals from North Atlantic populations.     

Heat tolerance,growth and regeneration in three North Sea bryozoans exposed to different constant temperatures

Three species of bryozoans—Membranipora membranacea (L.), Electra pilosa (L.) and Conopeum reticulum (L.) — are capable of acclimating to elevated temperatures, above the normal range experienced in nature, when exposed to a gradual increase in ambient temperature. Conspicuous differences in LD 50 values, as a consequence of acclimation, occur between representatives of the same species acclimated and grown at constant temperatures in the laboratory. The tolerance range of these species is influenced by their thermal history in the laboratory. While increased ambient temperatures accelerate growth rate, final colony size attained after prolonged exposure declines at higher temperatures. The size of zooecia attained is inversely proportional to the test temperature. Colonies of E. pilosa maintained at 22°C develop erect branches. Hence, it is probable that E. pilosa forma erecta is only a growth form of normally encrusting colonies of E. pilosa. Temperature affects rate of regeneration.     

Differential sensitivities to hypoxia by two anoxia-tolerant marine molluscs: A biochemical analysis

The metabolic responses to a series of low oxygen tensions were compared for two species of Mediterranaean bivalves,Mytilus galloprovincialis andScapharca inaequivalvis. Whereas both species have well-developed and similar tolerances of anoxia, the metabolic responses ofS. inaequivalvis to low oxygen tensions indicate a substantially greater tolerance of hypoxia. Compared withM. galloprovincialis, the responses ofS. inaequivalvis included the ability to maintain a constant oxygen consumption down to a much lower pO₂ value (ca. 1.7 vs 3.4 ppm), and a lower critical pO₂ for the recruitment of fermentative pathways of ATP production (ca. 1 vs 3 ppm). Furthermore, a graded increase in the output of anaerobic products (succinate, alanine) occured at oxygen tensions below 3 ppm inM. galloprovincialis and reached a maximum at 1.6 ppm whereas inS. inaequivalvis the net accumulation of anaerobic products at the lowest oxygen tension tested (0.5 ppm) was still substantially less than the level of production output in complete anoxia. This suggests that fermentative pathways are maximally activated at all oxygen tensions below 1.6 ppm inM. galloprovincialis whereas rates of anaerobic pathways are still less than maximum at 0.5 ppm inS. inaequivalvis. These results indicate that in situations of declining oxygen tensions, such as occur due to eutrophication,M. galloprovincialis would not only begin to experience metabolic stress at higher oxygen tensions thanS. inaequivalvis but would experience greater stress at any given pO₂. Such differences in hypoxia tolerances may explain the success of the recently introducedS. inaequivalvis in out-competing the nativeM. galloprovincialis in the Adriatic Sea.This research was conducted at the Consorzio di Studi, Richerche ed Interventi sulle Risorse Marine, Viale Amerigo Vespucci 2, I-47042 Cesenatico (FO), Italy. Delta Institute for Hydrobiological Research, Yerseke, The Netherlands. Publication no. 554     

Upper temperature tolerances of some European molluscs

The upper temperature tolerances of three European species of Cardium [C. (Cerastoderma) glaucum Bruguière, C. tuberculatum L., C. (Cerastoderma) edule L.] are compared by means of median lethal temperature (LT₅₀) and median burial temperature (BT₅₀) determinations for periods of exposure up to 96 h. The influence of previous acclimation temperatures on these determinations is also considered. C. glaucum from shallow water (0.5 to 1 m), lagoonal, habitats in the Mediterranean Sea shows a greater thermal tolerance than C. tuberculatum from deeper water (4 to 5 m) in the Mediterranean. The thermal tolerance of C. edule from the intertidal zone, but at higher latitudes, is intermediate. Young C. glaucum show a greater resistance to short exposures to high temperatures than adults, but for longer exposures their tolerance is the same. All 3 species exhibit a significant effect of previous acclimation temperature on the burrowing response, and C. glaucum and C. tuberculatum a significant but lesser effect on LT₅₀. LT₅₀ determinations with C. edule showed secondary mortality effects which may have obscured any effect of acclimation temperature.     

Susceptibility to oxidative stress of the Mediterranean demosponge Petrosia ficiformis : role of endosymbionts and solar irradiance

 The effects of elevated pO₂ and irradiance as inducers of prooxidant conditions have been investigated in the Mediterranean demosponge Petrosia ficiformis (Poiret, 1789). This species lives symbiotically with the autotrophic cyanobacterium Aphanocapsa feldmanni, the abundance of which is controlled by the intensity of light irradiance. In the presence of symbionts, tissues of P. ficiformis were characterized by a general enhancement of antioxidant defenses as compared to aposymbiotic specimens. The main differences included higher activities of several antioxidant enzymes and a greater capability to neutralize various forms of oxyradicals, as indicated by the total oxyradical scavenging capacity (TOSC) assay. Elevated pO₂, more than light, appeared to be the primary factor inducing prooxidant pressure in the Mediterranean sponge; in fact, irrespective of the solar irradiance experienced by the sponge, symbiotic specimens showed comparable activities of antioxidant enzymes and a similar scavenging capacity towards various reactive oxygen species. However, the potential toxicity of photodynamic production of reactive oxygen species was demonstrated in organisms from more irradiated sites, as the levels of antioxidant defenses were lowered in the outer layer of the sponge. The role of enhanced antioxidant defenses in protecting symbiotic specimens, also from oxyradical-mediated toxicity of light exposure, was supported by translocation experiments; aposymbiotic sponges did not survive when moved to conditions of elevated solar irradiance, while no effects were observed in symbiotic specimens if translocated and/or deprived of symbionts. Received: 23 November 1999 / Accepted: 13 June 2000     

Some aspects of the thermal tolerance of Trichomya hirsuta (Mollusca: Bivalvia) of Eastern Australia

The upper temperature tolerance range for Trichomya hirsuta L. is described for acclimation temperatures of 10° to 32°C at 30% S. Changes in thermal resistance with time are described along with the incipient lethal temperatures. The eurythermicity for the species is 240.7 C°-squared. The ultimate upper incipient lethal temperature is 35.1°C. Definition of the incipient sublethal temperature is given, and is equal to 32°C. Diet effects are shown not to be significant in short-term lethal experiments, but indicate that unfed mussels reduce their resistance after prolonged exposure to high temperatures. Size was also shown to have no effect on resistance and tolerance. A comparison of the tolerance triangle of T. hirsuta with those of the temperate species Mytilus edulis and Mya arenaria revealed that the 24-h LT₅₀ minus 2.2 C° approximates the incipient lethal temperature. The eurythermicities of the temperate species are Mytilus edulis, 363 C°-squared; and Mya arenaria, 415 C°-squared.     

Influence of anoxia on adaptation of euryhaline polychaetes to hyposmotic conditions

The metabolic reactions ofArenicola marina andNereis diversicolor (both euryoxic and euryhaline polychaetes from the intertidal) to hyposmotic shock under anaerobic conditions were investigated in 1987–1988 using specimens from the East Frisian Wadden Sea. Although reductions in salinity were within the limits of tolerance under normoxic conditions, during anoxia they resulted in increased stress and a significant reduction in survival time. Both species were unable to sufficiently intensify anaerobic energy production to match the increased requirement for energy during adaptation to hyposmotic conditions. Moreover, as an adaptation to anoxic conditions, worms reduced their metabolic activity after the first 6 h. Thus, specimens remained more swollen than at the same reduction in salinity under normoxic conditions. InA. marina only the extracellular volume was reduced all be it to a limited extent.N. diversicolor probably reacted in the same or similar way. In both species, cells remained swollen. The concentrations of cellular free amino acids were not reduced; that means the main mechanism of cellular volume regulation was not activated under these conditions.     

Dehydrogenases as tools in the study of marine sediments

A method is outlined for the measurement of NADH₂-dependent dehydrogenase activity in whole samples as well as in fractions of carbonate sediments. The method is based on extraction of enzyme activity with phosphate buffer containing 0.12% Triton X-100, dialysis, and a photometric assay which permits initial velocity determinations of the enzyme reaction under controlled conditions of pH, temperature, and substrate concentration. The dehydrogenases extracted from carbonate sediment of a subtropical beach at Bermuda are characterized by low K _m values (0.03 to 0.07 mM NADH₂/1), pH maxima around 8.5, and temperature maxima between 35° and 40°C. Their vertical distribution in the sediment agrees with what is known about the distribution of biomass on beaches of this type, maximum activity occurring in the topmost centimetre. Approximately 80 to 90% of the total electron transport activity is contained in the grain fraction, the remainder in the interstitial fraction of a sediment sample. From this it can be inferred that the interstitial fauna contributes only little to the total energy budget of this type of sediment, which is dominated by the Aufwuchs on the sand grains. The electron transport activity (ETA) measured by means of the dehydrogenase assay is taken to represent the maximum transport capacity (ETC) of all the organisms living in the sand ecosystem. From published evidence it is inferred that oxygen consumption of sediment samples and of individual organisms measured in vivo usually accounts for 10 to 20% of the maximum electron transport capacity measured in vitro with saturating concentrations of substrates and with Triton X-100 as part of the enzyme assay. It is suggested further that the ratios of dehydrogenase activities in different fractions or zones of sediment, or of different organisms, may represent one of the best indicators, so far available, of energy relationships in marine sediments.Contribution No. 652 from the Bermuda Biological Station for Research.     

Upper temperature tolerances of some European molluscs II. Donax vittatus,D. semistriatus and D. trunculus

The upper temperature tolerances of 3 European species of Donax [D. vittatus (da Costa), D. semistriatus Poli, D. trunculus L.] are compared by means of median lethal temperatures (LT₅₀) and median burial temperature (BT₅₀) determinations for periods of exposure up to 96 h. The influence of previous acclimation temperatures on these determinations is also considered. D. trunculus shows the greatest thermal tolerance, reflecting its distribution in shallower water; D. vittatus and D. semistriatus display much closer thermal tolerances, although D. semistriatus which has a more southerly geographical distribution has a slightly higher thermal tolerance. All 3 species exhibit a significant effect of previous acclimation temperature, the effect on the burrowing responses being greater than that on LT₅₀.     

Oxygen/sulfide regime and nematode fauna associated with Arenicola marina burrows: new insights in the thiobios case

Profiles of oxygen and sulfide around the burrows of the lugworm, Arenicola marina, from a North Sea tidal flat were examined with microelectrodes, and the steep gradients were related to the microdistribution of nematodes. Around the tail shaft free oxygen penetrated only 2 mm into the burrow wall, coinciding with a bright zone sharply limited by the ambient black sediment. Contrastingly, in normal bottoms of the tidal flat (controls) only the surface of the bright zone was supplied with free oxygen. Here, the dark colouration coincided with the presence of free hydrogen sulfide. Around the tail shaft the nearest free hydrogen sulfide was detected 6 mm from the burrow wall leaving several millimetres of black sediment without measurable free sulfide. We discuss how these divergencies may relate to the stability of the oxygen/sulfide gradients and the course of time involved in their formation. A total of 54 nematode species were identified. Based on non-metric Multidimensional Scaling Ordination, four nematode assemblages corresponded to four microhabitats of the A. marina burrow: the funnel, the feeding pocket, the tail shaft and the feacal cast. The tail shaft assemblage (oxic plus partly anoxic zones) was similar to that of the anoxic zone of the control sediment. It was dominated by the most abundant nematode in the present study, Metalinhomoeus biformis (mean abundance in tail shaft 202 indx10 cm^-3). Adults of common nematode species from sulfidic microhabitats had a significantly higher length/diameter ratio than those inhabiting the oxic zone of the control sediment (p<0.001). The chemical recordings and metric analysis indicate that these slender nematodes around the A. marina tail shaft and in the reduced horizons of the reference sites represent thiobiotic assemblages, as compared to the shorter and stouter oxybiotic species characterising the assemblages from the surface zone and (partly) the funnel.     

Studies on the causes of mortality of the estuarine bivalve Macoma balthica under conditions of (near) anoxia

Survival of the bivalve Macoma balthica in (near) anoxic seawater was studied in a static system and a flow-through system and compared with emersed exposure to air and N₂. In the static system, a decrease in pH and exponential accumulation of sulphide in the incubation medium were observed, indicating excessive growth of (sulphate-reducing) bacteria. These changes in the chemical environment were prevented by the use of a flow-through system. However, this treatment hardly affected survival time. Median mortality times were 8.3 and 9.0 days for the static and flow-through incubation, respectively. Addition of the antibiotic chloramphenicol strongly increased survival time in both systems with corresponding values of 17.9 and 23.0 days. A similar value was obtained for survival in air (LT₅₀= 21.7 days). In a second experiment (1 year later), we obtained much lower values for anoxic survival in a static system, although laboratory conditions, season and temperature were similar. The pH values were adjusted to 6.5, 7.2 and 8.2 by buffering the media (25 mM Tris-HCl), and the corresponding LT₅₀ values were 5.5, 5.7 and 4.7 days, respectively. In the presence of chloramphenicol the values were 10.8, 10.9 and 9.5 days, respectively. These values show that a slightly acidic medium increased survival time. Exposure to an atmosphere of N₂ resulted in a survival time close to that in anoxic seawater without chloramphenicol (LT₅₀= 6.4 days). Overall the results indicate that proliferation of anaerobic bacteria associated with the bivalves was the main cause of death. Since chloramphenicol also displayed a strong positive effect in the flow-through system, which prevented the accumulation of released waste products and a decrease of pH, bacterial damage must have been by injury of the tissues of the clams and not by the release of noxious compounds to the medium. Bacterial outbreaks are a part of every anoxic event (eutrophication), and therefore, in their habitats, direct bacterial infection may also be the cause of clam mortality. It is concluded that laboratory studies on anoxic tolerance, or impact of sulphide, may produce artefacts when no precautions are taken to suppress bacterial proliferation. Received: 4 July 2000 / Accepted: 6 December 2000     

Physioecology of zooplankton. I. Effects of phytoplankton concentration,temperature, and body size on the growth rate of Calanus pacificus and Pseudocalanus sp.

Changes in dry weight and in weight-specific growth rates were measured for copepodite stages of Calanus pacificus Brodsky and Pseudocalanus sp. cultured under various combinations of phytoplankton concentration and temperature. Mean dry weight of early copepodites was relatively unaffected by either food concentration or temperature, but mean dry weight of late stages increased hyperbolically with food concentration and was inversely related to temperature. The food concentration at which maximum body weight was attained increased with increasing temperature and body size, and it was considerably higher for C. pacificus than for Pseudocalanus sp. This suggests that final body size of small species of copepods may be determined primarily by temperature, whereas final body size of large species may be more dependent on food concentration than on temperature. Individual body weight increased sigmoidally with age. The weight-specific growth rate increased hyperbolically with food concentration. The maximum growth rate decreased logarithmically with a linear increase in body weight, and the slope of the lines was proportional to temperature. The critical food concentration for growth increased with body size proportionally more at high than at low temperature, and it was considerably higher for C. pacificus than for Pseudocalanus sp. Because of these interactions, early copepodites optimized growth at high temperature, even at low food concentrations, but under similar food conditions late stages attained higher growth at low temperature. The same growth patterns were found for both species, but the rates were significantly higher for the larger species, C. pacificus, than for the smaller one, Pseudocalanus sp. On the basis of findings in this study and of analyses of relationships between the maximum growth rate, body size, and temperature from other studies it is postulated (1) that the extrapolation of growth rates from one species to another on the basis of similarity in body size is not justified, even for taxonomically related species; (2) that the allometric model is inadequate for describing the relationship between the maximum weight-specific growth rate and body size at the intraspecific level; (3) that the body-size dependence of this rate is strongly influenced by temperature; and (4) that species of zooplankton seem to be geographically and vertically distributed, in relation to body size and food availability, to optimize growth rates at various stages of their life cycles.Contribution No. 1127 from the Department of Oceanography, University of Washington, Seattle, Washington 98195, USA     

Oxygen uptake and heat production in a metabolic conformer (Littorina irrorata) and a metabolic regulator (Uca pugnax)

The heat production of Littorina irrorata and Uca pugnax in air was measured with a twin calorimeter while oxygen tension was measured with a pO₂ electrode. Both L. irrorata, an oxyconformer, and U. pugnax, a metabolic regulator, showed a rapid decrease in oxygen uptake (below 1.3 mm Hg in L. irrorata and 13.4 mm Hg in U. pugnax) while heat production decreased more slowly. Consequently, during the period of minimum oxygen uptake, the oxycalorific coefficient increased from about 4.8 for both species to an average value of 8.3 in L. irrorata and 19.9 cal ml^-1 O₂ in U. pugnax, indicating the onset of anaerobic metabolism and accumulation of metabolic and products. Above their respective critical pO₂, the oxycalorific coefficient was the same as the commonly used conversion factor of 4.8 cal ml^-1 O₂. From one time interval to the next, however, the coefficient varied from 3.8 to 5.4 in L. irrorata and from 2.9 to 6.0 in U. pugnax, indicating, that the processes of oxygen consumption and heat production are more or less independent of each other and usually not in phase.     

Life history of the nematode Theristus anoxybioticus from sublittoral muddy sediment at methane seepages in the northern Kattegat,Denmark

Field and laboratory studies from 1989 to 1994 of the nematode Theristus (Penzancia) anoxybioticus Jensen, 1995 inhabiting muddy sediment at methane seepages in the northern Kattegat, Denmark, have revealed a series of biological features of adults and juveniles not observed before in free-living marine nematodes. Reproductive adults were present in April and May only and inhabited the uppermost cm of sediment, while juveniles inhabited deep anoxic and sulphidic sediment layers during the remaining months of the year. This points to a downwards migration of newly hatched juveniles and an upwards migration during adulthood. Gut content analyses showed that adults feed mainly on benthic diatoms by swallowing whole cells while juveniles probably feed on bacteria; this differentiation in food clearly relates to the main bulk of potential food items in their respective microhabitats. The generation time is estimated to be one year, with a juvenile life span of about nine months, which is four to eight times longer than that found in related aerobic species of similar body size. Adults survived in oxic water but 50% died within 15 h in hypoxic water (5 to 6% atm sat), and all died within 12 h in anoxic water. Juveniles on the other hand died within 0.5 h in oxic water but survived anoxic water for at least 15 d. These results suggest that juveniles of T. anoxybioticus are adapted to an anaerobic life style.     

Effect of Water Variables On Lead Tolerance in Postlarvae of Penaeus Indicus (H. Milne Edwards)

Lead tolerance in Penaeus indicus post-larvae (PL) was studied in relation to the water variables: salinity, temperature and pH. the LC₅₀ for 96 hrs was 7.22 ppm at ambient conditions of salinity (20%_o), temperature (29°C) and pH (7.2). the post-larvae were found to be sensitive to salinity variations with a significant (P < 0.05) low LC₅₀ values at lower (2%_o) and higher (29%_o) ranges. Though a decrease in LC₅₀ value was observed both at higher (45°C) and lower (10°C) temperatures, it was significantly (P < 0.05) low only at higher temperature indicating more toxicity. the LC₅₀ values also showed a significant (P < 0.05) decrease in acidic (pH 2.8) and alkaline (pH 11.0) conditions. the data indicate that lead toxicity increases in the PL of P. indicus with variations in the water variables.     

In situ respiration of benthic communities in Castle Harbor,Bermuda

In situ measurements of community respiration were made at two stations in Castle Harbor, Bermuda, during April and May, 1971. Total community respiration was 20.67 and 19.11 ml O₂ m^-2 h^-1 at Stations 1 and 2, respectively, in April. In May, respiration increased with water temperature to 26.99 and 24.56 ml O₂ m^-2 h^-1. Significant differences (P<0.05) existed between stations and sampling periods. Bacterial respiration was estimated from sediment treatment with streptomycin-SO₄. Values ranged from 7.71 to 8.72 ml O₂ m^-2 h^-1 in April and May, respectively. No significant difference existed between sampling periods or stations. No detectable chemical O₂ demand of the sediment, determined by a formalin treatment, was found. Total community respiration was further compartmentalized into macrofaunal, meiofaunal, and microfaunal-microfloral components. Both the macrofaunal and meiofaunal respiration was negligible compared to that estimated for the microfaunal-microfloral component.Contribution No. 2708 from the Woods Hole Oceanographic Institution, and Contribution No. 552 from the Bermuda Biology Station. This study was supported in part by National Science Foundation Grants GZ 1508 and GB 16161.     

Temperature and plankton

The relationship between temperature and metabolism was studied in Artic copepods with regard to the concept of metabolic cold adaptation of polar poikilotherms. Temperature tolerance and respiration rates of the dominant copepods Calanus finmarchicus (Gunnerus), C. glacialis (Jaschnov), C. hyperboreus (Krøyer) and Metridia longa (Lubbeck), collected in Fram Strait, Greenland Sea, in July 1983, were studied at different temperatures. Temperature tolerance in the boreal C. finmarchicus was slightly higher than in the three Arctic species. Respiration rates at lower temperatures followed the Arrhenius equation in all species, with values for (temperature characteristics) between 11.05 and 22.95, corresponding to a Q₁₀ between 2.05 and 4.5. This increase in metabolic rate with rising temperature was not related to an increase of swimming activity, as was shown by videoanalysis. Activity was determined as average swimming speed and as frequency of certain locomotor patterns. Average swimming speed remained unchanged at all temperatures and was ca 1 cm s^-1 for all species, when only periods of active swimming were considered. The time spent with active swimming did not change with temperature in M. longa and C. finmarchicus, but decreased in c. glacialis. In C. hyperboreus it increased at 5°C and decreased again at higher temperatures. It is suggested that the increase in oxygen consumption is fully accounted for by the basal metabolism.     

Nephtys hombergii, a free-living predator in marine sediments: energy production under environmental stress

Nephtys hombergii is a free-living, burrowing predator in marine sediments. The worm is, therefore, exposed to various environmental conditions which tube-dwelling polychaetes of the same habitat most likely do not encounter. The worms have to survive periods of severe hypoxia and sulphide exposure, while at the same time, they have to maintain agility in order to feed on other invertebrates. N. hombergii is adapted to these conditions by utilising several strategies. The species has a remarkably high content of phosphagen (phosphoglycocyamine), which is the primary energy source during periods of environmental stress. With increasing hypoxia, energy is also provided via anaerobic glycolysis (pO₂<7 kPa), with strombine as the main end-product. Energy production via the succinate pathway becomes important only under severe hypoxia (<2 kPa), suggesting a biphasic response to low oxygen conditions which probably is related to the worm's mode of life. The presence of sulphide resulted in a higher anaerobic energy flux and a more pronounced energy production via glycolysis than in anoxia alone. Nevertheless, after sulphide exposure under anaerobic conditions of <24 h, N. hombergii is able to recover completely. Although N. hombergii appears to be well adapted to a habitat with short-term fluctuations in oxygen and appearance of hydrogen sulphide, its high energy demand as a predator renders it likely to limit its survival in an environment with longer lasting anoxia and concomitant sulphide exposure. Received: 28 May 1997 / Accepted: 21 June 1997